BEEBE, Ark. — Preliminary autopsies on 17 of the up to 5,000 blackbirds that fell on this town indicate they died of blunt trauma to their organs, the state’s top veterinarian told NBC News on Monday.

Their stomachs were empty, which rules out poison, Dr. George Badley said, and they died in midair, not on impact with the ground.

That evidence, and the fact that the red-winged blackbirds fly in close flocks, suggests they suffered some massive midair collision, he added. That lends weight to theories that they were startled by something.

Earlier Monday, the estimated number of dead birds was raised to between 4,000 and 5,000, up sharply from the initial estimate of 1,000.